Popular smoking articles, such as cigarettes, have a substantially cylindrical rod-shaped structure and include a charge, roll or column of smokable material, such as shredded tobacco (e.g., in cut filler form), surrounded by a paper wrapper, thereby forming a so-called “smokable rod” or “tobacco rod.” Normally, a cigarette has a cylindrical filter element aligned in an end-to-end relationship with the tobacco rod. Typically, a filter element comprises plasticized cellulose acetate tow circumscribed by a paper material known as “plug wrap.” Typically, the filter element is attached to one end of the tobacco rod using a circumscribing wrapping material known as “tipping paper.” It also has become desirable to perforate the tipping material and plug wrap, in order to provide dilution of drawn mainstream smoke with ambient air. Descriptions of cigarettes and the various components thereof are set forth in Tobacco Production, Chemistry and Technology, Davis et al. (Eds.) (1999). A cigarette is employed by a smoker by lighting one end thereof and burning the tobacco rod. The smoker then receives mainstream smoke into his/her mouth by drawing on the opposite end (e.g., the filter end) of the cigarette.
Certain filter elements for cigarettes contain materials that alter the chemical composition or sensory characteristics of mainstream smoke. For example, it is known to incorporate certain adsorbent materials into a filter element, such as activated carbon or charcoal materials (collectively, carbonaceous materials) in particulate or granular form. Granules of carbonaceous material can be incorporated into “dalmation” types of filter regions using the general types of techniques used for traditional dalmation filter manufacture. Techniques for production of dalmation filters are known, and representative dalmation filters have been provided commercially by Filtrona Greensboro Inc. Alternatively, granules of carbonaceous material can be incorporated into “cavity” types of filter regions using the general types of techniques used for traditional “cavity” filter manufacture. Various types of filters incorporating charcoal particles or activated carbon types of materials are set forth in U.S. Pat. No. 2,881,770 to Touey; U.S. Pat. No. 3,101,723 to Seligman et al.; U.S. Pat. No. 3,236,244 to Irby et al.; U.S. Pat. No. 3,311,519 to Touey et al.; U.S. Pat. No. 3,313,306 to Berger; U.S. Pat. No. 3,347,247 to Lloyd; U.S. Pat. No. 3,349,780 to Sublett et al.; U.S. Pat. No. 3,370,595 to Davis et al.; U.S. Pat. No. 3,413,982 to Sublett et al.; U.S. Pat. No. 3,551,256 to Watson; U.S. Pat. No. 3,602,231 to Dock; U.S. Pat. No. 3,972,335 to Tigglebeck et al.; U.S. Pat. No. 5,360,023 to Blakley et al.; U.S. Pat. No. 5,909,736 to Stpyridis; and U.S. Pat. No. 6,537,186 to Veluz; US Pat. Publication Nos. 2003/0034085 to Spiers et al.; 2003/0106562 to Chatterjee; 2006/0025292 to Hicks et al.; and 2007/0056600 to Coleman, III et al.; PCT WO 2006/064371 to Banerjea et al.; PCT WO 2006/051422 to Jupe et al.; and PCT WO2006/103404 to Cashmore et al., which are incorporated herein by reference.
In another example, oxidation catalysts have been incorporated into a filter element of a smoking article in order to alter the chemistry of mainstream smoke passing through the filter element. In particular, oxidation catalysts that convert carbon monoxide to carbon dioxide are known in the art. Exemplary catalyst materials are set forth in U.S. Pat. No. 4,317,460 to Dale et al.; U.S. Pat. No. 7,549,427 to Dellinger et al; and U.S. Pat. No. 7,560,410 to Pillai et al., which are incorporated herein by reference. Maintaining a high level of smoke-altering catalytic activity can be challenging for certain oxidation catalysts because some catalyst materials are quickly deactivated by exposure to tar or water present in mainstream smoke.
It would be highly desirable to provide a filter element for a smoking article that includes a smoke-altering material capable of altering the chemical makeup or sensory characteristics of mainstream smoke, and which is designed to minimize the negative impact of certain components of mainstream smoke on performance of the smoke-altering material.